In conventional aircraft engines, engine controllers, such as full authority digital engine controllers (FADECs), control certain operating characteristics of the engines to enhance the engines' performance. For example, FADECs typically include a digital computer, known as an electronic engine control unit (ECU) and a variety of sensors that measure, for example, various environmental and engine conditions such as engine temperature, engine fluid pressures, air temperature, and air density. During operation of the engine, the ECU receives data signals from the sensors and calculates engine operating parameters based upon the data signals. Based upon the engine operating parameters, the FADEC controls certain engine components, such as the engine's fuel injection system and ignition timing, to adjust the engine's fuel usage and optimize the engine's performance.
For example, as each aircraft engine cylinder assembly receives a fuel and air mixture, a spark plug associated with each aircraft engine cylinder assembly ignites the fuel and air mixture. Under normal operating conditions, the spark plug initiates combustion of the fuel and air mixture when an associated crankshaft positions a piston of the cylinder assembly within about 15 to 40 degrees before a top dead center (TDC) position, the point of maximum compression of the fuel and air mixture. Ignition of the fuel and air mixture at a time prior to the piston reaching the TDC position maximizes the pressure required to displace the piston within a cylinder assembly housing to drive the crankshaft.
In order to cause or adjust the ignition of the fuel and air mixture at a time before the piston reaches a TDC position, the ECU must identify the rotational position or angle of the crankshaft along with the crankshaft's angular velocity. Accordingly, conventional aircraft engines utilize a detection system to detect the positioning and speed of the crankshaft. For example, in a conventional aircraft engine, the crankshaft includes a gear reduction assembly located at a rear portion of engine (i.e., the portion opposing the propeller) and a sensor positioned in proximity to the gear reduction assembly. The gear reduction assembly turns at a rate that is half of the angular velocity of the crankshaft. Accordingly, the sensor detects the half-rate rotation of the gear reduction assembly and provides an output signal, indicative of the crankshaft position and angular velocity, to the ECU. The ECU utilizes the output signal to approximate the position of each cylinder within each cylinder assembly and to adjust the spark timing for the cylinder.